SU1165967A1 - Method of measuring moisture content - Google Patents

Abstract

METHOD OF MEASURING MOISTURE solids using a capacitive three-electrode sensor, which implies that the electrodes are mounted on the object in the same plane and on the same axis, the second electrode being positioned between the first and third electrodes so that the distance between the first and second electrodes is less than nor between the second and third electrodes, alternating voltage is applied to the electrodes, the capacitance between the electrode pairs is measured and the moisture content of the material is calculated from the capacitance measurement results In order to improve the measurement accuracy by eliminating the influence on the measurement result of the parameters of the surface layer of a substance, voltages of the same frequency and phase are applied to three electrodes, the voltage amplitude between the first and second electrodes is changed and, when the minimum capacitance value is reached they are made from a measurement of the capacitances between the electrode pa (lm.

Description

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FIG. The invention relates to physicotechnical measurements and can be used to measure the moisture content of materials of heterogeneous thickness. A known method for measuring humidity by creating an electric field in the material between coplanar electrodes of a capacitive sensor and measuring its capacitance 1. The disadvantage of this method is the low measurement accuracy due to the strong influence of the quality of the material surface. The closest to the invention to the technical essence is a method for measuring the moisture content of solids using a capacitive three-electrode sensor, namely, that the electrodes are mounted on the object under investigation in one plane and on the same axis, the second electrode being positioned between the first and third electrodes so that the distance between the first and second electrodes is less than the distance between the second and third electrodes, alternating voltage is applied to the electrodes, the capacitance between the electrode pairs is measured and, as a result The tatam of capacitance measurement calculates the moisture content of material 2. A disadvantage of this method is that it is impossible to exclude the results of measurements of the surface layer of variable thickness, due to the large non-linear sensitivity of the sensor with coplanar electrodes to the dielectric properties of material layers located at different depths. The purpose of the invention is to improve the measurement accuracy by eliminating the effect on the measurement result of the parameters of the surface layer of a substance. This goal is achieved by the fact that according to the method of measuring the moisture content of solids using a capacitive three-electrode sensor, the principle is that the electrodes are mounted on the test object in the same plane and on the same axis, the second electrode being positioned between the first and third electrodes so that the distance between the first and second electrodes is less than the distance between the second and third electrodes, alternating voltage is applied to the electrodes, the capacitance between the electrode pairs is measured and, based on the measurement results Capacity calculated moisture material is fed to the three electrode voltages of the same frequency and phase, an amplitude is varied between a first voltage and a second electrode and an achievement of a minimum value of capacitance between them is produced, measurement of capacitance between the electrode pairs. FIG. 1 shows the spatial distribution of electric fields in the layer of the material under study using a three-electrode sensor; in fig. 2 - block device that implements the proposed method. The three-electrode sensor consists of electrodes 1-3 placed on the object under study 4. At the same time, two electric fields are created - the main and the additional one. The main field created between electrodes 1 and 3, under the action of the potential difference fi - fj, has a relatively large depth of penetration into the object. The additional field created between electrodes 1 and 2, under the action of the potential difference Af -fz-fi, has a relatively small depth. If f2 1 О the power lines of the additional field are directed towards the power lines of the main field, therefore, in the surface layer of the material of the object, due to the superposition of the fields, they are mutually compensated. By adjusting the magnitude of the potential fa on the electrode 2, the strength of the additional field is changed, and its penetration depth changes, which makes it possible to compensate the main field to a predetermined depth. In this case, the capacitance between electrodes 1 and 3 is measured and when the capacitance reaches its minimum value, the total capacitance C of the sensor is calculated by the formula Cx Cs + / C „+ C, j - Cjj. where C is the ballast capacitance of the sensor (substrate, wires, etc.); Sc-own partial capacitance of electrode 1; C, c is a partial capacitance between electrodes 1 and 3; C1g, partial capacitance between electrodes 1 and 2. Next, based on the measurement results Cx, the humidity of the material is determined. Since the electric field generated by the coplanar system of electrodes is maximal on the surface of the material and nonlinearly decreases in its thickness, the surface layer of the material of the object makes a significant contribution to the capacitance of the SC and Cij, the dielectric properties of which can differ significantly from the rest of the material mass. Capacity is entirely determined by the properties of the surface layer of the material. By regulating the voltage on the electrode 2, the results of measurements of the surface layer of the material are almost completely eliminated. The meter 5 of the container is connected to the measuring electrode 1. Between the measuring electrode 1 and the guard electrode 2

connected in series are a voltage follower 6 and an amplifier 7. The amplifier 7 is made with a variable acceleration factor from 1 to 1.5.

As a result of the superposition of opposing fields in the surface layer of the material, the field is absent; therefore, the change in the properties of this layer as well as the quality of the surface does not

influences the measurement results of capacitance between electrodes 1 and 3.

Improving the accuracy and reliability of measurement results by the proposed method allows to reduce the total number of measurement results in the study of objects for humidity and thereby increase labor productivity.

Claims (1)

METHOD FOR MEASURING HUMIDITY OF SOLIDS using a capacitive three-electrode sensor, which consists in the fact that the electrodes are mounted on the test object in one plane and on the same axis, the second electrode being placed between the first and third electrodes so that the distance between the first and second electrodes is less the distance between the second and third electrodes, an alternating voltage is applied to the electrodes, the capacitance between the electrode pairs is measured, and the moisture content of the material is calculated from the capacitance measurements, excellent in that, in order to increase the accuracy of the measurement by eliminating the influence of the parameters of the surface layer of the substance on the measurement result, voltages of the same frequency and phase are applied to the three electrodes, the voltage amplitude is changed between the first and second electrodes, and upon reaching the minimum capacitance between them, g measurement of capacitances between electrode pairs. SU „„ 1165967